U.S. Pat. No. 6,233,818 to Finn et al. discloses a method of manufacturing an RFID inlay. More specifically, this patent discloses a process and device for the contacting of a wire conductor in the course of the manufacture of a transponder unit arranged on a substrate and comprising a wire coil and a chip unit such as a chip module with terminal areas. By virtue of the process according to the invention described in this prior art, there is no longer any necessity, with a view to bringing the terminal areas of the chip unit into contact with the ends of the coil to provide a separate contact substrate on which enlarged terminal areas are formed. Rather, the coil substrate, which is used as substrate for the wire coil and which, for example in the case where the transponder unit is intended to serve for the manufacture of a chip card, is formed by means of a plastic support sheet corresponding to the dimensions of the chip card, serves as a contacting or positioning aid for the relative positioning of the ends of the coil in relation to the terminal areas of the chip unit. In this case the chip unit may either be arranged in a recess in the substrate provided for this purpose or may be provided on the surface of the substrate. The first alternative affords the possibility of arranging the chip unit in the recess optionally prior to fixation of the wire conductors or of introducing the chip unit into the recess only after fixation of the wire conductors, in order subsequently to implement the actual contacting of the wire conductors on the terminal areas.
More specifically, in this prior art, firstly an antenna is applied to the substrate via a wiring device using ultrasound to attach the wire to the substrate. An antenna is thereby formed with an initial antenna region and a final antenna region, both regions traversing a window shaped-substrate recess. Then, a chip module is placed in the recess whereby terminal contact areas of the module abut the initial and terminal antenna regions. Subsequently, an electrical connection is realized between the terminal contact areas and the initial and final antenna regions of the antenna by means of a thermode which, under the influence of pressure and temperature, creates a connection by material closure between the wire antenna and the terminal contact areas of the chip (this is also called thermo compression).
EP patent application 2 001 077 discloses a method for producing a device comprising a transponder antenna connected to contact pads and a device obtained by said process. Specifically, an antenna with terminal connections is provided in contact with a substrate. Contact pads are placed on the substrate and connected to the terminal sections of the antenna. The connection is produced by means of a soldering step by introducing energy between the pads and the terminal sections. The pads are placed such as to provide a surface facing an antenna terminal connection section. The section is arranged on the substrate and the soldering energy is directly applied to the pads. A cavity is produced in the substrate close to the antenna terminal sections and a microcircuit is inserted at least partly in the cavity with contact pads positioned facing the antenna terminal sections. Finally a soldering step is carried out using thermo-compression or ultrasound. To carry out this soldering step, an anvil is used that goes through a reinforcing sheet or layer opposite the terminal section to provide a support during the soldering operation. This process therefore imposes the creation of a hole for the anvil which has to be carefully placed to correspond to the position of the terminal section.
The inventions disclosed in the publication cited above all use chip modules. By definition, a chip module is much larger than a chip per se and the module also comprises much larger connection pads. A typical chip module for contactless inlay is the mob6 from NXP, presenting a surface area of 8100×5100 μm for a thickness of 300 μm, with connection pads having a surface area of 1500×5100 μm each.
U.S. Pat. No. 5,572,410 discloses a chip being directly connected to wire antenna. In this patent, a wire is wound around a core and the two ends of the wire are soldered to metal paths deposited over the active layer of the chip. This technology, which is called “direct bonding”, minimizes the size of the resulting transponder and the number of its constituting elements, and as a consequence the related production costs.
The metal paths which are extensions of the usual small pads of the chips, are called megabumps (or megapads) and have a dimension adapted to the connection of the antenna wire (which has typically a diameter of 60-80 μm). For example, a typical chip used for such applications is the Hitag μ from NXP, wherein the chip surface area is of 550×550 μm for 150 μm thickness and the megabump show a surface area of 294×164 μm (while the original pads are only 60×60 μm).
It also has to be noted that in the particular application disclosed in this patent, the antenna is not embedded in a support layer but wound around a ferrite core. The resulting transponder has a resonant frequency of about 125 kHz and the antenna show over 300 turns. This does not require a fine tuning of the antenna, and its spires are just wound one onto the other at high speed.
However, if one wants to work at a higher frequency, for example 13.56 MHz, one will have to control the shape and the relative spacing of each spire in order to correctly tune the antenna. Wire embedding is the most efficient and popular technology for manufacturing of high frequency wire antennas, but up to now, this was made exclusively by using chip modules. This introduces an important limitation as the resulting inlay cannot be thinner than the used module.
The manufacturing of thinner high frequency inlays is the main motivation to try to combine direct bonding and wire embedding technologies.
Table 1 proposes a list of some of the high frequency chips on the market which could be used for direct bonding. These chips present much smaller dimensions (not only in thickness) in comparison to the mob6 from NXP described above.
TABLE 1examples of high frequency chips applicable for direct bondingChipChipBumpsBumpTotaldimsthicknessdimsthicknessthickness SupplierRef.[μm][μm][μm][μm][μm]EMEM42331034 × 1054100, 200 or300 × 40018N/A280NXPMF CLASSIC 1k650 × 675 150164 × 29418168INSIDEPicopass 2k V1.21198 × 1192280310 × 71220300NXPP60D080/P60D144 VA2166 × 300475600 × 600 1287INSIDEAT90SC28880RCFV2740 × 297075600 × 6801287
The problem one is confronted with is to be able to handle such small chips properly while in the same time the antenna wire is fixed on a large sheet of plastic. Solutions used today for chip modules (which are much heavier and larger than single chips) are not usable anymore at such large manufacturing scale.
A solution to this problem has been disclosed in PCT application No. PCT/EP2012/063671 filed on Jul. 12, 2012 in the name of ASSA ABLOY AB, now published under the number WO 2014/008937 A1 the content of this earlier application being entirely incorporated by reference in the present application.
In this prior application, an aim was to manufacture the thinner RFID inlay possible by direct bonding of a chip, such as a RFID chip, to a wire antenna that was embedded in a substrate.
This allowed forming a high frequency RFID monolayer that is thinner than the sum of the thickness of the chip plus the thickness of the antenna (chip and antenna being inside the carrier monolayer itself).
Other HF RFID technologies known in the art and using a naked chip as flip chip technology will be thicker due to the fact that they need a carrier layer without holes where the antenna (etched antenna or screen printed antenna) will be put on. After this step, a chip is connected on the antenna and the final thickness will be the addition of the chip thickness+antenna thickness+ carrier layer thickness. In this case, a carrier layer has to be added to the total thickness of the layer, a disadvantage that is not present anymore when using the principle of the invention as described in the present application.
According to one aspect, the invention of WO 2014/008937 was directed to a method of direct bonding an embedded wire antenna to a chip whereby the tooling allowed at the same time to hold the chip from one side and to connect the antenna wires to said chip through a connection head, such as a welding head, from the other side.
More precisely, the method described in this prior art reference comprised at least the following steps:                providing a support layer with at least a first and a second side;        embedding at least one wire antenna in the support layer;        processing the support layer with said embedded wire antenna(s) to a connection station in which        the support layer is approached on the first side by a holding device holding at least one chip with a surface comprising connection pads;        the support layer is approached on the second side by a connection device; and        the antenna(s) wire is (are) connected to the connection pads by means of a reciprocal pressure exerted between the holding device and the connection device.        
In the prior art method, the support layer with the wire embedded antenna may be processed along a processing path and the holding device and the connection device both may approach the support layer by movements essentially perpendicular to said processing path.